The present invention relates to a carboxymethyl cellulose slurry and a process for the preparation thereof.
Carboxymethyl cellulose (CMC) is often used in the form of its sodium salt for modifying the rheologic properties of aqueous liquids. The applications to be considered are the clarification of water, the treatment of minerals, the thickening of foodstuffs and medication, the thickening of farm products, the use in oil drilling liquids, the use in building materials, such as concrete, the modification of ceramic materials, the modification of latex colours, the use in paper coating and the use as a protective colloid in emulsion and suspension polymerization.
CMC has conventionally been delivered in a dry, particulate form. The drawbacks thereof are the formation of dust, the poor dispersing in aqueous liquids and the long dissolution times when CMC is dissolved in water.
The same problems are encountered with the treatment of CMC type powders as generally with dry particulate materials. Since CMC type powders are hygroscopic and absorb moisture from the air their particles can therefore become agglomerated. It is very difficult to disperse agglomerated particles in aqueous liquids. The dissolution of CMC powder is difficult in other respects, too, since the powder tends, during dissolution, to form an agglomerate, the gel on the surface of which prevents water from penetrating into the dry powder inside the agglomerate and from dissolving it.
For the above-mentioned reasons, users of CMC products tend to require them in a form in which they can be easily dissolved in the aqueous system of their process.
The FI-application 885969 presents the delivery of CMC products e.g. in the form of such aqueous dispersions that contain particulate CMC product, polyethylene glycol having a low molecular mass (LWPEG), water and polyethylene glycol having a high molecular mass (HWPEG). LWPEG was defined in the publication as a substituted or non-substituted polyethylene glycol being liquid at room temperature and having a molar mass of about 200 to 700 g/mol. HWPEG was defined as a substituted or non-substituted polyethylene glycol being solid at room temperature and having a molar mass of over 3000 g/mol.
According to the examples of the publication the part of the CMC(Na-salt)-product in the whole mixture counts for 20 to 23% by weight. The part of LWPEG counts for 41 to 48% by weight, the part of water counts for 29 to 33% by weight and the part of HWPEG counts for 3 to 4.5% by weight. The molar masses of the LWPEG-samples used were 200, 300, and 400 g/mol. The molar mass of the HWPEG-samples used was 20,000 g/mol.
The drawback of the product presented in the FI-publication mentioned is that its maximum CMC content giving a sufficiently flowing but stable dispersion, is only about 20% by weight. Despite this, the product according to the publication has a very low dispersion stability. Of the CMC dispersions prepared in the examples only two were stable after 24 hours from the time of preparation. It is clear that such a product cannot be used after storage and transport without cumbersome redispersion.